tesseract/textord/scanedg.cpp

/**********************************************************************
 * File:        scanedg.c  (Formerly scanedge.c)
 * Description: Raster scanning crack based edge extractor.
 * Author:					Ray Smith
 * Created:					Fri Mar 22 16:11:50 GMT 1991
 *
 * (C) Copyright 1991, Hewlett-Packard Ltd.
 ** Licensed under the Apache License, Version 2.0 (the "License");
 ** you may not use this file except in compliance with the License.
 ** You may obtain a copy of the License at
 ** http://www.apache.org/licenses/LICENSE-2.0
 ** Unless required by applicable law or agreed to in writing, software
 ** distributed under the License is distributed on an "AS IS" BASIS,
 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 ** See the License for the specific language governing permissions and
 ** limitations under the License.
 *
 **********************************************************************/

#include "mfcpch.h"
#include          "edgloop.h"
//#include                                      "dirtab.h"
#include          "scanedg.h"

#define WHITE_PIX     1          /*thresholded colours */
#define BLACK_PIX     0
                                 /*W->B->W */
#define FLIP_COLOUR(pix)  (1-(pix))

#define EWSIZE        4          /*edge operator size */

#define XMARGIN       2          //margin needed
#define YMARGIN       3          //by edge detector

                                 /*local freelist */
static CRACKEDGE *free_cracks = NULL;

/**********************************************************************
 * block_edges
 *
 * Extract edges from a PDBLK.
 **********************************************************************/

DLLSYM void block_edges(                      //get edges in a block
                        IMAGE *t_image,       //threshold image
                        PDBLK *block,         //block in image
                        ICOORD page_tr        //corner of page
                       ) {
  uinT8 margin;                  //margin colour
  inT16 x;                       //line coords
  inT16 y;                       //current line
  ICOORD bleft;                  //bounding box
  ICOORD tright;
  ICOORD block_bleft;            //bounding box
  ICOORD block_tright;
  int xindex;                    //index to pixel
  BLOCK_LINE_IT line_it = block; //line iterator
  IMAGELINE bwline;              //thresholded line
                                 //lines in progress
  CRACKEDGE **ptrline = new CRACKEDGE*[t_image->get_xsize()+1];
  block->bounding_box (bleft, tright); // block box
  block_bleft = bleft;
  block_tright = tright;
  for (x = tright.x () - bleft.x (); x >= 0; x--)
    ptrline[x] = NULL;           //no lines in progress

  bwline.init (t_image->get_xsize());

  margin = WHITE_PIX;

  for (y = tright.y () - 1; y >= bleft.y () - 1; y--) {
    if (y >= block_bleft.y () && y < block_tright.y ()) {
      t_image->get_line (bleft.x (), y, tright.x () - bleft.x (), &bwline,
        0);
      make_margins (block, &line_it, bwline.pixels, margin, bleft.x (),
        tright.x (), y);
    }
    else {
      x = tright.x () - bleft.x ();
      for (xindex = 0; xindex < x; xindex++)
        bwline.pixels[xindex] = margin;
    }
    line_edges (bleft.x (), y, tright.x () - bleft.x (),
      margin, bwline.pixels, ptrline);
  }

  free_crackedges(free_cracks);  //really free them
  free_cracks = NULL;
  delete[] ptrline;
}


/**********************************************************************
 * make_margins
 *
 * Get an image line and set to margin non-text pixels.
 **********************************************************************/

void make_margins(                         //get a line
                  PDBLK *block,            //block in image
                  BLOCK_LINE_IT *line_it,  //for old style
                  uinT8 *pixels,           //pixels to strip
                  uinT8 margin,            //white-out pixel
                  inT16 left,              //block edges
                  inT16 right,
                  inT16 y                  //line coord
                 ) {
  PB_LINE_IT *lines;
  ICOORDELT_LIST *segments;      //bits of a line
  ICOORDELT_IT seg_it;
  inT32 start;                   //of segment
  inT16 xext;                    //of segment
  int xindex;                    //index to pixel

  if (block->poly_block () != NULL) {
    lines = new PB_LINE_IT (block->poly_block ());
    segments = lines->get_line (y);
    if (!segments->empty ()) {
      seg_it.set_to_list (segments);
      seg_it.mark_cycle_pt ();
      start = seg_it.data ()->x ();
      xext = seg_it.data ()->y ();
      for (xindex = left; xindex < right; xindex++) {
        if (xindex >= start && !seg_it.cycled_list ()) {
          xindex = start + xext - 1;
          seg_it.forward ();
          start = seg_it.data ()->x ();
          xext = seg_it.data ()->y ();
        }
        else
          pixels[xindex - left] = margin;
      }
    }
    else {
      for (xindex = left; xindex < right; xindex++)
        pixels[xindex - left] = margin;
    }
    delete segments;
    delete lines;
  }
  else {
    start = line_it->get_line (y, xext);
    for (xindex = left; xindex < start; xindex++)
      pixels[xindex - left] = margin;
    for (xindex = start + xext; xindex < right; xindex++)
      pixels[xindex - left] = margin;
  }
}


/**********************************************************************
 * whiteout_block
 *
 * Extract edges from a PDBLK.
 **********************************************************************/

void whiteout_block(                 //clean it
                    IMAGE *t_image,  //threshold image
                    PDBLK *block     //block in image
                   ) {
  inT16 x;                       //line coords
  inT16 y;                       //current line
  inT16 xext;                    //line width
  int xindex;                    //index to pixel
  uinT8 *dest;                   //destination pixel
  TBOX block_box;                 //bounding box
  BLOCK_LINE_IT line_it = block; //line iterator
  IMAGELINE bwline;              //thresholded line

  block_box = block->bounding_box ();
  for (y = block_box.bottom (); y < block_box.top (); y++) {
                                 //find line limits
    x = line_it.get_line (y, xext);
    t_image->get_line (x, y, xext, &bwline, 0);
    dest = bwline.pixels;        //destination pixel
    for (xindex = 0; xindex < xext; xindex++)
      *dest++ = 1;
    t_image->put_line (x, y, xext, &bwline, 0);
  }
}


/**********************************************************************
 * line_edges
 *
 * Scan a line for edges and update the edges in progress.
 * When edges close into loops, send them for approximation.
 **********************************************************************/

void
line_edges (                     //scan for edges
inT16 x,                         //coord of line start
inT16 y,                         //coord of line
inT16 xext,                      //width of line
uinT8 uppercolour,               //start of prev line
uinT8 * bwpos,                   //thresholded line
CRACKEDGE ** prevline            //edges in progress
) {
  int xpos;                      //current x coord
  int xmax;                      //max x coord
  int colour;                    //of current pixel
  int prevcolour;                //of previous pixel
  CRACKEDGE *current;            //current h edge
  CRACKEDGE *newcurrent;         //new h edge

  xmax = x + xext;               //max allowable coord
  prevcolour = uppercolour;      //forced plain margin
  current = NULL;                //nothing yet

                                 //do each pixel
  for (xpos = x; xpos < xmax; xpos++, prevline++) {
    colour = *bwpos++;           //current pixel
    if (*prevline != NULL) {
                                 //changed above
                                 //change colour
      uppercolour = FLIP_COLOUR (uppercolour);
      if (colour == prevcolour) {
        if (colour == uppercolour) {
                                 //finish a line
          join_edges(current, *prevline);
          current = NULL;        //no edge now
        }
        else
                                 //new horiz edge
          current = h_edge (xpos, y, uppercolour - colour, *prevline);
        *prevline = NULL;        //no change this time
      }
      else {
        if (colour == uppercolour)
          *prevline = v_edge (xpos, y, colour - prevcolour, *prevline);
                                 //8 vs 4 connection
        else if (colour == WHITE_PIX) {
          join_edges(current, *prevline);
          current = h_edge (xpos, y, uppercolour - colour, NULL);
          *prevline = v_edge (xpos, y, colour - prevcolour, current);
        }
        else {
          newcurrent = h_edge (xpos, y, uppercolour - colour, *prevline);
          *prevline = v_edge (xpos, y, colour - prevcolour, current);
          current = newcurrent;  //right going h edge
        }
        prevcolour = colour;     //remember new colour
      }
    }
    else {
      if (colour != prevcolour) {
        *prevline = current =
          v_edge (xpos, y, colour - prevcolour, current);
        prevcolour = colour;
      }
      if (colour != uppercolour)
        current = h_edge (xpos, y, uppercolour - colour, current);
      else
        current = NULL;          //no edge now
    }
  }
  if (current != NULL) {
                                 //out of block
    if (*prevline != NULL) {     //got one to join to?
      join_edges(current, *prevline);
      *prevline = NULL;          //tidy now
    }
    else {
                                 //fake vertical
      *prevline = v_edge (xpos, y, FLIP_COLOUR(prevcolour)-prevcolour, current);
    }
  }
  else if (*prevline != NULL)
                                 //continue fake
    *prevline = v_edge (xpos, y, FLIP_COLOUR(prevcolour)-prevcolour, *prevline);
}


/**********************************************************************
 * h_edge
 *
 * Create a new horizontal CRACKEDGE and join it to the given edge.
 **********************************************************************/

CRACKEDGE *
h_edge (                         //horizontal edge
inT16 x,                         //xposition
inT16 y,                         //y position
inT8 sign,                       //sign of edge
CRACKEDGE * join                 //edge to join to
) {
  CRACKEDGE *newpt;              //return value

  //      check_mem("h_edge",JUSTCHECKS);
  if (free_cracks != NULL) {
    newpt = free_cracks;
    free_cracks = newpt->next;   //get one fast
  }
  else {
    newpt = new CRACKEDGE;
  }
  newpt->pos.set_y (y + 1);      //coords of pt
  newpt->stepy = 0;              //edge is horizontal

  if (sign > 0) {
    newpt->pos.set_x (x + 1);    //start location
    newpt->stepx = -1;
    newpt->stepdir = 0;
  }
  else {
    newpt->pos.set_x (x);        //start location
    newpt->stepx = 1;
    newpt->stepdir = 2;
  }

  if (join == NULL) {
    newpt->next = newpt;         //ptrs to other ends
    newpt->prev = newpt;
  }
  else {
    if (newpt->pos.x () + newpt->stepx == join->pos.x ()
    && newpt->pos.y () == join->pos.y ()) {
      newpt->prev = join->prev;  //update other ends
      newpt->prev->next = newpt;
      newpt->next = join;        //join up
      join->prev = newpt;
    }
    else {
      newpt->next = join->next;  //update other ends
      newpt->next->prev = newpt;
      newpt->prev = join;        //join up
      join->next = newpt;
    }
  }
  return newpt;
}


/**********************************************************************
 * v_edge
 *
 * Create a new vertical CRACKEDGE and join it to the given edge.
 **********************************************************************/

CRACKEDGE *
v_edge (                         //vertical edge
inT16 x,                         //xposition
inT16 y,                         //y position
inT8 sign,                       //sign of edge
CRACKEDGE * join                 //edge to join to
) {
  CRACKEDGE *newpt;              //return value

  if (free_cracks != NULL) {
    newpt = free_cracks;
    free_cracks = newpt->next;   //get one fast
  }
  else {
    newpt = new CRACKEDGE;
  }
  newpt->pos.set_x (x);          //coords of pt
  newpt->stepx = 0;              //edge is vertical

  if (sign > 0) {
    newpt->pos.set_y (y);        //start location
    newpt->stepy = 1;
    newpt->stepdir = 3;
  }
  else {
    newpt->pos.set_y (y + 1);    //start location
    newpt->stepy = -1;
    newpt->stepdir = 1;
  }

  if (join == NULL) {
    newpt->next = newpt;         //ptrs to other ends
    newpt->prev = newpt;
  }
  else {
    if (newpt->pos.x () == join->pos.x ()
    && newpt->pos.y () + newpt->stepy == join->pos.y ()) {
      newpt->prev = join->prev;  //update other ends
      newpt->prev->next = newpt;
      newpt->next = join;        //join up
      join->prev = newpt;
    }
    else {
      newpt->next = join->next;  //update other ends
      newpt->next->prev = newpt;
      newpt->prev = join;        //join up
      join->next = newpt;
    }
  }
  return newpt;
}


/**********************************************************************
 * join_edges
 *
 * Join 2 edges together. Send the outline for approximation when a
 * closed loop is formed.
 **********************************************************************/

void join_edges(                   //join edge fragments
                CRACKEDGE *edge1,  //edges to join
                CRACKEDGE *edge2   //no specific order
               ) {
  CRACKEDGE *tempedge;           //for exchanging

  if (edge1->pos.x () + edge1->stepx != edge2->pos.x ()
  || edge1->pos.y () + edge1->stepy != edge2->pos.y ()) {
    tempedge = edge1;
    edge1 = edge2;               //swap araound
    edge2 = tempedge;
  }

  //      tprintf("Joining %x=(%d,%d)+(%d,%d)->%x<-%x ",
  //              edge1,edge1->pos.x(),edge1->pos.y(),edge1->stepx,edge1->stepy,
  //              edge1->next,edge1->prev);
  //      tprintf("to %x=(%d,%d)+(%d,%d)->%x<-%x\n",
  //              edge2,edge2->pos.x(),edge2->pos.y(),edge2->stepx,edge2->stepy,
  //              edge2->next,edge2->prev);
  if (edge1->next == edge2) {
                                 //already closed
    complete_edge(edge1);  //approximate it
                                 //attach freelist to end
    edge1->prev->next = free_cracks;
    free_cracks = edge1;         //and free list
  }
  else {
                                 //update opposite ends
    edge2->prev->next = edge1->next;
    edge1->next->prev = edge2->prev;
    edge1->next = edge2;         //make joins
    edge2->prev = edge1;
  }
}


/**********************************************************************
 * free_crackedges
 *
 * Really free the CRACKEDGEs by giving them back to delete.
 **********************************************************************/

void free_crackedges(                  //really free them
                     CRACKEDGE *start  //start of loop
                    ) {
  CRACKEDGE *current;            //current edge to free
  CRACKEDGE *next;               //next one to free

  for (current = start; current != NULL; current = next) {
    next = current->next;
    delete current;              //delete them all
  }
}